A group wearing reflective rain gear approaches the exit of the San Jacinto Tunnel after taking a tour on Thursday, Feb. 26 2015 in Cabazon. The tunnel carries Colorado River water from the aqueduct to the San Jacinto Valley.

A group heads down the San Jacinto Tunnel during a tour Thursday, Feb. 26, 2015, in Cabazon. The tunnel carries Colorado River water from the aqueduct to the San Jacinto Valley. Metropolitan Water District used to close the tunnel every five to eight years for cleaning and inspection but now does so every year.

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A group prepares to head into the San Jacinto Tunnel for a tour on Thursday, Feb. 26 2015 in Cabazon. Metropolitan Water District closes the tunnel once a year for cleaning and inspection, giving a few guests the opportunity for a tour.

A group including Craig Miller, deputy general manager for Western Municipal Water District, left; Rosa Castro, inspector trip specialist for Metropolitan Water District, middle; and Andrew Walcker, board member for the Riverside Public Utilities, prepare to tour the San Jacinto Tunnel on Thursday, Feb. 26, 2015.

Brian Jaramillo, President of Tilden-Coil Constructors, left, and Andrew Walcker, a Riverside Public Utilities board member, walk out of the San Jacinto Tunnel after taking a tour on Thursday, Feb. 26 2015 in Cabazon. The tunnel carries Colorado River water from the aqueduct to the San Jacinto Valley.

A group walks into the San Jacinto Tunnel for a tour on Thursday, Feb. 26, 2015, at the northeast entrance in Cabazon. The tunnel is part of the Colorado River Aqueduct.

Once a year for the past dozen years, the mighty Colorado River Aqueduct has been squeezed closed at Lake Havasu, large steel doors have swung open against a shoulder of Mount San Jacinto in Cabazon and a select group of visitors have entered a 13.4-mile-long time machine.

The visitors board a nine-passenger cart pulled by a small tractor and take a tour – inspection trip, the Metropolitan Water District calls it – inside the San Jacinto Tunnel.

The tunnel, dug between 1933 and 1939, carries water from the aqueduct through the mountain to an outlet just north of San Jacinto. The water then moves on to customers in the southern reaches of Southern California.

When the water is running, the tunnel carries as much as 1,750 cubic feet a second. It would fill three Olympic-size swimming pools in less time than it takes to read this sentence.

When the water isn’t running, a period stretching just over two weeks of the winter, cleaning and repair crews rush in. And Metropolitan directors invite 30 to 45 VIPs to take a ride on the inspection tram. Passage is so limited there was not even room for a reporter to ride.

The guests – mostly engineers and other officials from member agencies served by Metropolitan – don hard hats, boots and rain slickers with reflective tape that provides an eery, bug-like glow as they walk through the dark tunnel toward the light.

The aqueduct, owned and operated by Metropolitan, was shut down Feb. 17 this year and reopened March 6. The doors providing access to the San Jacinto Tunnel won’t reopen for another 12 months, Metropolitan officials noted, so they go to extremes to make sure no visitor is left behind.

Each visitor writes his or her name on a baggage tag attached to a padlock. The padlock is fastened to a bright red ammo can near the portal entrance and the visitor takes the only key to the lock. Each visitor must keep his or her own key. The doors to the portal remain open until every padlock is reopened by its holder and the baggage tag removed.

(Hover over infographic for timeline information. Story continues below.)

‘A WILD RIVERS EXPERIENCE’

The journey inside the tunnel looks from the entrance like a Disney attraction: a small train making its way through a 16-foot-diameter corridor with relatively smooth walls looking like sprayed concrete over a floor containing a small stream of water.

“It’s really just a concrete tunnel,” said Andrew Walker, a member of Riverside’s public utilities board who took the tour. “There is a little bit of water. It does come in through some of the sides of the concrete tunnel. It looks like little hoses of water coming at you. It’s kind of a Wild Rivers experience.”

The water entering the tunnel is actually groundwater and its presence is a big part of the tunnel’s history.

Construction crews dug and blasted their way through the mountain, extending about three miles into it before water “started gushing in,” said Steve Heathcoat, 54, a third-generation Metropolitan employee who is in charge of maintenance of the delivery system from Indio to Perris and Moreno Valley to Winchester.

“There were two fault zones along the tunnel,” he said. “As they got closer to those, it was more likely to have water intrusion.”

Groundwater leaking into the tunnel triggered a legal battle that lasted more than half a century, with a local Indian tribe, the Soboba Band of Luiseño Indians, contending that their wells dried up.

It was a legal battle that was not resolved for more than seven decades, with President George W. Bush signing a bill in 2008 that called, among other things, for the federal government to contribute $10 million of the $17 million settlement. The tribe received cash, water and land, Heathcoat said.

ENGINEERING ON DISPLAY

Construction of the tunnel was far from easy, Heathcoat said, with two private contractors eventually fired before Metropolitan took over the operation itself.

Original plans called for a tunnel that bored straight through the mountain, but workmen discovered places where the rock was so fractured or hard that it was faster and easier to detour.

The walls were shored up with steel in some places and wood in others, as a rail car transported workmen and equipment to construct 20- to 30-foot sections of the tunnel.

“It was amazing to see the amount of construction and the perfection for that era, back in the ’30s,” said Brenda Dennstedt, a Western Municipal Water District board member who took the tour.

The walls were “absolutely smooth,” she said. “The engineering down there is fascinating. There is some shading differences in there as you go through the tunnel” that give an almost luminescent appearance.

“I thought there would be a lot more imperfections in the craftsmanship of it,” Dennstedt said. “But not at all. I was really surprised.”

That is central to the purpose of the inspection tours, said Tom Evans, a board member of both the Western Municipal and Metropolitan water districts. He was making his third tour of the tunnel.

“We do these to help our customers and community members understand the value of these facilities and how much we depend on them,” he said. “I renew my appreciation for the courage of the people who built it. They were digging … 13 miles through solid rock and having to blast their way through – not knowing what they were headed for, as far as water being there.”

A BRUSH AND A LASER

The real work during the shutdown, sandwiched around the tours, involved using a machine with large brushes to scrub the inside of the tunnel and keep it running efficiently, Heathcoat said.

Until 2003, the tunnel was opened, inspected and cleaned only once every five to eight years, said Metropolitan spokesman Bob Muir.

As pumps along the aqueduct were improved, the capacity of the aqueduct increased. Between that and a drought at the aqueduct’s source that has lingered since 2003, Muir said, Metropolitan has discovered that it can shut down the flow, scour the tunnel and resume pumping water without a disruption in service to its customers.

Maintenance workers are trying something new this year, Heathcoat said.

Besides the cleaning machinery, they sent a 3D laser through, taking careful measurements of the circumference of the horseshoe-shaped tunnel. The measurements will eventually be compared with the original plans for the tunnel to make sure the dimensions have not changed and that no dirt or debris is left behind on the walls.

If the tunnel has narrowed, they will adjust their cleaning plans next year, Heathcoat said.

Engineers did find something that wasn’t supposed to be there.

A 5- to 6-foot-long snake, possibly a red racer, had slithered three miles into the tunnel. It apparently wandered in when they opened the gates to clean the tunnel.

The snake was Heathcoat’s biggest surprise since the time they found a military bomb in one of their siphons in Desert Hot Springs. It turned out to be inert, he said, apparently used for practice.